1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to an ultraviolet (UV) irradiating device for hardening a sealant that is at least partially curable by the application of ultraviolet light and a method of manufacturing an LCD device using the same.
2. Discussion of the Related Art
Generally, ultra thin flat panel displays having a display screen with a thickness of several centimeters or less, and in particular, flat panel LCD devices, are widely used in monitors for notebook computers, spacecraft, and aircraft because such LCD devices have low power consumption and are easy to carry.
Such an LCD devices include a lower substrate, an upper substrate, and a liquid crystal layer. A thin film transistor (TFT) and a pixel electrode are formed on the lower substrate. The upper substrate is formed to oppose the lower substrate. A light-shielding layer, a color filter layer, and a common electrode are formed on the upper substrate. The common electrode may also be formed on the lower substrate for an in plane switching LCD device. The liquid crystal layer is between the lower and upper substrates. In operation, an electric field is formed between the lower and upper substrates by the pixel electrode and the common electrode so that the liquid crystal layer is “driven” to be aligned according to the direction of the electric field. Light transmittivity is controlled through driving liquid crystal layer so that a picture image is displayed.
In the aforementioned LCD device, to form a liquid crystal layer between lower and upper substrates, a vacuum injection method based on capillary phenomenon and pressure difference has been conventionally used.
A related art method of manufacturing an LCD device based on a vacuum injection method will be described.
First, a lower substrate provided with a TFT and a pixel electrode and an upper substrate provided with a light-shielding layer, a color filter layer, and a common electrode are manufactured.
To maintain a uniform cell gap between the lower and upper substrates, a spacer is formed on one of the lower and upper substrates. A sealant is formed on the corner of one substrate so that a liquid crystal is prevented from leaking out and both substrates are bonded to each other. At this time, a thermal hardening sealant such as an epoxy sealant is used as the sealant.
The lower and upper substrates are bonded to each other. The epoxy sealant is manufactured by mixing epoxy resin with an initiator. If the epoxy sealant is heated, the epoxy resin activated by the initiator is polymerized by cross-linkage so as to provide excellent adherence.
The bonded substrates are placed in a vacuum chamber to maintain the substrates under the vacuum state and then are dipped in the liquid crystal. If the substrates are maintained under the vacuum state, the liquid crystal is injected into the substrates by capillary action.
Nitrogen gas (N2) is injected into the vacuum chamber after the liquid crystal is appropriately filled in the substrates, causing a pressure difference between the inside of the substrates and the outside of the substrates, and liquid crystal is thereby filled into empty spaces between the substrates. Thus, the liquid crystal layer is finally formed between both substrates.
However, such a vacuum injection method has a problem in that it takes a relatively long time to inject the liquid crystal between the substrates, particularly for devices having a large display area, thereby reducing the productivity.
To solve such a problem, a liquid crystal application method has been developed. A brief description is included here to assist in understanding the present invention and will now be described with reference to FIGS. 1A to 1D.
As shown in FIG. 1A, a lower substrate 1 and an upper substrate 3 are prepared. A plurality of gate and data lines (not shown) are formed on the lower substrate 1. The gate lines cross the data lines to define a pixel region. A thin film transistor (not shown) is formed at each crossing point between the gate and data lines. A pixel electrode (not shown) connected with the thin film transistor is formed in the pixel region.
A light-shielding layer (not shown) is formed on the upper substrate 3 to prevent light from leaking out from the gate and data lines and the thin film transistor. Color filter layers (not shown) of red(R), green(G), and blue(B) are formed on the light-shielding layer, and a common electrode (not shown) is formed on the color filter layers. In the case of an in plane switching LCD device, the common electrode is provided on the lower substrate. An alignment film (not shown) is formed on at least one of the lower substrate 1 and the upper substrate 3 to initially align a liquid crystal to be applied.
As shown in FIG. 1B, a sealant 7 is formed on the lower substrate 1 and a liquid crystal 5 is applied thereon, so that a liquid crystal layer is formed. A spacer (not shown) is disposed on the upper substrate 3 to maintain a cell gap.
As shown in FIG. 1C, the lower substrate 1 and the upper substrate 3 are bonded each other.
At this time, in the method of manufacturing the LCD device based on the vacuum injection method, a bonding process of both substrates is performed before the liquid crystal is injected. On the other hand, in the method of manufacturing the LCD device based on the liquid crystal application method, a bonding process of both substrates is performed after the liquid crystal 5 is applied. Therefore, if a thermal hardening sealant is used as the sealant 7, the liquid crystal expand and 7 may flow out when it is heated. For this reason, a problem arises in that the liquid crystal 5 is contaminated.
Therefore, in the method of manufacturing the LCD based on the liquid crystal application method, a sealant at least partially curable by ultraviolet (UV) light is used as the sealant 7.
As shown in FIG. 1D, a UV light source 9 is vertically irradiated so that the sealant 7 is hardened.
Meanwhile, FIGS. 2A to 2D illustrate a difference of a hardening rate of a sealant according to a pattern of a light-shielding layer and the sealant formed on a substrate.
As shown in FIG. 2A, the sealant 7 is formed outside a region where the light-shielding layer 8 is formed. In this case, UV light is incident upon the sealant 7 even if the UV light is irradiated on the upper substrate 3 where the light-shielding layer 8 is formed.
However, as shown in FIG. 2B, if the sealant 7 is formed to overlap the light-shielding layer 8, the UV light is not incident upon the sealant in the overlapped region. For this reason, the sealant in the overlapped region is not hardened. Thus, adherence between the lower substrate 1 and the upper substrate 3 is reduced.
As shown in FIG. 2C, if the sealant 7 is formed inside the light-shielding layer 8, the UV light is incident upon the upper substrate 3, the light-shielding layer 8 is formed, and the sealant 7 is not irradiated with the UV light. Therefore, the UV light should also be irradiated upon the lower substrate 1 to sufficiently cure the sealant 7 from below. However, as shown in FIG. 2D, if a metal line layer such as a gate line 6a and/or a data line 6b on the lower substrate 1 overlaps the sealant 7, the UV light is not incident upon the sealant 7 in region A. For this reason, the sealant 7 is not hardened, and adherence between the lower substrate 1 and the upper substrate 3 is reduced.
In other words, if the light-shielding layer or the metal line layer is formed overlapping the sealant 7, the UV light is not incident upon the sealant. As a result, adherence between the lower substrate and the upper substrate is reduced.